1. Technical Field
The present invention relates to a semiconductor device, a liquid discharge head, and a liquid discharge apparatus.
2. Related Art
As a semiconductor device, a device which is provided for controlling a head of a liquid discharge apparatus (for example, a printer) is known. Drive elements (for example, piezo elements) are provided for each nozzle in a head of a printer. A semiconductor device for controlling a head controls an application of a drive signal to each of the piezo elements. More specifically, a drive signal is applied to the piezo element after selecting a pulse of the drive signal with a printing switch provided in the semiconductor device.
In addition, a device which detects a state (such as defective nozzle) of a nozzle by detecting a residual vibration signal after the application of a drive signal has been proposed in the related art (for example, refer to JP-A-2013-233704). A detection switch for detecting the residual vibration is provided on a side opposite to the printing switch viewed from the piezo element. The printing switch and the detection switch are configured to have a printing transistor (corresponding to discharge transistor) and a detection transistor, respectively.
As described above, when a detection switch is provided on an opposite side to a printing switch viewed from a piezo element, a semiconductor device in which the detection switch is provided is separated from a semiconductor device in which the printing switch is provided. In contrast, when the detection switch is provided on the same side as the printing switch viewed from the piezo element, it is possible to provide the printing switch and the detection switch in the same semiconductor device.
Meanwhile, it takes time to charge or discharge a piezo element when resistance of a printing transistor configuring the printing switch increases, thereby lowering a printing speed. In addition, when the resistance of the printing transistor increases, heat generated when charging or discharging the piezo element becomes a problem. Therefore, it is necessary to lower the resistance of the printing transistor. That is, a size of the printing transistor is increased. A protection resistor cannot be added to the printing transistor which is effective in reducing damage caused by an application of static electricity from the outside due to reduction in resistance according to the above-mentioned needs. However, the printing transistor is configured to reduce the damage by dispersing received static electricity on a large area using a large size of transistor.
Since the size of the printing transistor is large, when providing the detection switch and the printing switch in the same semiconductor device, a layout or a size of the detection switch becomes a problem. Specifically, the detection transistor configuring the detection switch does not need to allow a current to flow therein, and it is desirable to configure the detection transistor in a small transistor size for reduction in a layout area. However, when the size of the detection transistor is reduced, it is of concern that the detection transistor is destroyed by an application of static electricity.